This application seeks funding for the purchase of an SRI binocular, dual Purkinje-image, Eye Tracker to be used in several investigations of human visual sensitivity and oculomotility. The eye tracker will make it possible to conduct specific investigations of sensory and motor aspects of the visual systems of persons with normal and abnormal vision (e.g. amblyopes, nystagmats, and individuals with low vision). In making the requisite normal-abnormal comparisons, it is essential that stimuli be presented centrally and peripherally at known and verifiable retinal loci with the fixation, vergence, and accommodation mechanism free to act in their usual manner (for each subject) and with these mechanisms then placed in an appropriately open- loop state by the Eye Tracker. Specific issues that will be addressed with the requested instrumentation are: (1) how does interocular inhibition of amblyopes influence the monocular spatial abnormalities that underlie their acuity deficit (Flom); (2) does the reduced contrast sensitivity of anisometropic and strabismic amblyopes account for their decreased spatial position sensitivity, with spatial undersampling in strabismics additionally contributing to the deficit (Levi); (3) why is the visual world of congenital nystagmats stationary (Bedell); (4) do stereo-blind humans have vergence deficits, even subtle ones, that might result from absent or impaired disparity detectors (Crawford); (5) to what extent does the reduced vision of low vision patients influence their oculomotor control, and conversely (Loshin-White); (6) do surrounding contours affect resolution differently in anisometropic and strabismic amblyopes and/or does this contour interaction occur at different supra-retinal levels (Manny); is there a component of accommodation that normally continues to develop between 3 months and 4 years (Manny); (7) what role do eye movements play in the spectral characteristics of rivalry suppression (Smith-Harwerth); (8) how are spatial resolution and inhibitory interaction of isolated cone mechanisms across the retina affected by the normal eye movements during fixation (Physiological nystagmus) (Sperling); (9) what is the relation between precision of directionalization and optotype acuity and neural (grating) resolution (Wick).